The use of dosating apparatus to measure and transfer a defined volume of powder is well known. Typically the dosating apparatus comprises a dosator piston located in a sleeve, the dosator piston being retractable within the sleeve to create a cavity. The dosating apparatus is lowered into a powder reservoir to collect a sample of powder in the cavity and the powder is then ejected from the cavity into a suitable container.
Some of the problems involved in such a process concern optimisation of the fill accuracy and reproducibility, and reducing the aeration of the powder. Improvements to the dosating process made by prior art systems have typically involved either compacting the powder contained in the cavity or ensuring that air does not enter the cavity when filling. Compacting the powder when in the sleeve only compacts and reduces in size the sample already removed, improving packing but not the actual accuracy of the dose. Ensuring that air does not enter the cavity as the apparatus is lowered into the powder by retracting the dosator piston as the apparatus moves through the powder bed improves the filling to a certain extent but the density of the powder in the bed is not altered. A vacuum in the bottom of a powder reservoir may be used to improve the uniformity of the density of the bed. However, when the powder comprises a medicament and an excipient, the medicament particles are stripped from the excipient by the vacuum and a filter is required to capture the medicament particles.
The Applicants have found that the dose to dose repeatability and accuracy of the filling process can be improved by compacting the powder in the reservoir prior to removing the dose of powder to improve the uniformity of the density of the bed and to remove air from the bed. Compacting the powder in the bed prior to removing a sample has the advantage that the powder under the target is free to move within and away from the target area if necessary, leading to production of a bed with a more uniform density to ensure that all samples removed are of equal size.
The whole bed may be compacted prior to removal of the sample powder or alternatively small local areas of the bed may be compacted, corresponding to the area which will be removed. Compacting local areas of the bed has the advantage that the bed is easier to disrupt and prepare for the next round of sampling.